Re: [R] matching type question, please

[Rui Barradas]

Hello,

Inline.Às 23:29 de 16/12/21, Bert Gunter escreveu:
Not sure what you mean by this:

"But this only works if the vectors xr* are longer than xs*."

The solution I gave doesn't care about this.
a <- rbind(unique(z2),unique(z1))
a[duplicated(a),]
      xs1 xs2
## as before
Presumably you are referring to your use of match() (which is how %in%
is defined).
Yes, that's what I meant. It's probably more time and memory efficient 
to have cbind create a matrix of length(xr1) rows and extract the wanted 
ones with a logical index also of that length. The use of match() will 
avoid creating (maybe) longer data sets but it will raise the problem I 
mentioned.
Rui Barradas

Bert



On Thu, Dec 16, 2021 at 2:51 PM Rui Barradas <ruipbarra...@sapo.pt> wrote:
Hello,

And here is another solution, addressing the problem raised by Bert and
avoiding unique.


xr1 <- 8:0
xr2 <- 0:8
xs1 <- 9:3
xs2 <- 4
cbind(xr1, xr2)[(xr1 %in% xs1) & (xr2 %in% xs2),]
#xr1 xr2
#  4   4


xr1 <- c(1,2,1)
xr2 <- c(4,5,4)
xs1 <- c(6,6)
xs2 <- c(7,7)
cbind(xr1, xr2)[(xr1 %in% xs1) & (xr2 %in% xs2),]
#   xr1 xr2
(only column names are output)


But this only works if the vectors xr* are longer than xs*. Try swapping
the test values (both sets, Erin's original and Bert's) and see.

So here is a function that checks lengths first, then takes the right
branch.


dupSpecial <- function(x1, x2, y1, y2){
    if(length(x1) > length(y1)){
      cbind(x1, x2)[(x1 %in% y1) & (x2 %in% y2),]
    } else {
      cbind(y1, y2)[(y1 %in% x1) & (y2 %in% x2),]
    }
}
dupSpecial(xr1, xr2, xs1, xs2)


Hope this helps,

Rui Barradas


Às 22:01 de 16/12/21, Bert Gunter escreveu:
I am not sure Eric's solution is what is wanted:

Consider:
xr1 <- c(1,2,1)
xr2 <- c(4,5,4)
xs1 <- c(6,6)
xs2 <- c(7,7)

z1 <- cbind(xr1, xr2)
z2 <- cbind(xs1,xs2)
z1
       xr1 xr2
[1,]   1   4
[2,]   2   5
[3,]   1   4
z2
       xs1 xs2
[1,]   6   7
[2,]   6   7

If what is wanted is to find rows of z2 that match those in z1, Eric's
proposal gives (note the added comma to give a logical indexing
vector):

a <- cbind(c(xr1,xs1),c(xr2,xs2))
a[duplicated(a),]
       [,1] [,2]
[1,]    1    4
[2,]    6    7

This is obviously wrong, as it gives duplicates *within* z1 and z2,
not between them. To get rows of z2 that appear as duplicates of rows
of z1, then something like the following should do:

a <- rbind(unique(z1),unique(z2))
a
       xr1 xr2
[1,]   1   4
[2,]   2   5
[3,]   6   7
a[duplicated(a),]
       xr1 xr2
## nothing

I leave it to Erin to determine whether this is relevant to her
problem and, if so, how to fix up my suggestion appropriately.

Cheers,
Bert Gunter

"The trouble with having an open mind is that people keep coming along
and sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )

On Thu, Dec 16, 2021 at 12:39 PM Eric Berger <ericjber...@gmail.com> wrote:
a <- cbind(c(xr1,xs1),c(xr2,xs2))
a[duplicated(a)]
[1] 4 4


On Thu, Dec 16, 2021 at 10:18 PM Erin Hodgess <erinm.hodg...@gmail.com> wrote:
Hello!

I have the following:

   cbind(xr1,xr2)

        xr1 xr2

   [1,]   8   0

   [2,]   7   1

   [3,]   6   2

   [4,]   5   3

   [5,]   4   4

   [6,]   3   5

   [7,]   2   6

   [8,]   1   7

   [9,]   0   8

cbind(xs1,xs2)
       xs1 xs2

[1,]   9   4

[2,]   8   4

[3,]   7   4

[4,]   6   4

[5,]   5   4

[6,]   4   4

[7,]   3   4

These are ordered pairs.  I would like to get something that shows that the
pair (4,4) appears in both.  I have tried cbind with match and %in% and
intersect, but not getting the exact results.

Any suggestions would be appreciated.  I have a feeling that it's something
really easy that I'm just not seeing.

Thanks,
Erin


Erin Hodgess, PhD
mailto: erinm.hodg...@gmail.com

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